a) Field of the invention
The present invention relates to improvements made to the invention disclosed and claimed in U.S. Pat. No. 4,213,842 issued on Jul. 22, 1980 and Canadian patent No. 1,102,737 issued on Jun. 9, 1981, both in the name of the present inventor.
More particularly, the invention relates to an improved capping board incorporating pultruded filling bars.
b) Brief Description in the Prior Art
In the hydro-metallurgical industry, it is of common practice to electrically refine some metal in electrolytic cells especially devised for this purpose. Usually, the metal to be refined, or the metal used to carry the electric current, is in the form of plates of a given thickness which are provided at their upper end with two laterally extending projections. Such projections facilitate gripping, handling and hanging of the plates on the lateral sidewalls of the cells. In use, the plates, which can each weight several hundred pounds, are immersed into the cells in parallel relationship and are used as anodes, cathodes or both, depending on the affinity of the metal being refined.
In order to avoid damage to the masonry or concrete forming the lateral side walls of the cells during the insertion and removal of the heaving electrodes, it is a common practice to place a protective member, called "capping board", onto the top surface of each lateral sidewall of the cells. Such capping boards serve not only as a support but also as an insulator for the plates used as anodes or cathodes. Such capping boards also serve to position the plates with respect to each other and some of them may also be used as electric insulators between adjacent cells and/or the ground.
U.S. Pat. No. 4,213,842 and its Canadian counterpart No. 1,102,737 discloses and claims a capping board made of plastic material reinforced with glass fibers, which capping board is resistant to compression, abrasion, moisture, heat and corrosion and thus particularly useful to meet the industry requirements in terms of low costs, life span and reduced maintenance. More particularly, these patents disclose and claim a capping board molded from a plastic resin selected from the group consisting of polytetrafluoroethylene and polyester, vinylester, epoxy and phenolic resins resistant to corrosion by acids, to which are added from 10 to 20% by weight of glass fibers, from 2 to 10% by weight of silica, from 2 to 10% by weight of mica and from 2 to 10% by weight of feldspar.
According to a preferred embodiment of the invention disclosed in these patents, the glass fibers are in the form of a pressed mat or a woven cloth. This mat or cloth is impregnated with the selected resin in which mica has been added, and then is folded or layered in a mold so as to form a plurality of layers and give the desired shape to the capping board. During the folding operation, the cloth is reimpregnated with the selected resin and the silica mixed with the resin, in order to ensure a perfect adhesion between the layers.
According to another preferred embodiment of the invention disclosed in these patents, one or more wooden bars can be embedded in the capping board in order to reduce the quantities of resin and additives that are necessary for obtaining a thick capping board. Such use of wooden bars has proved so far to be very interesting in terms of manufacturing cost reduction. However, it has also proved to be a source of problems, especially because of their shrinkage on the overall length of the board, their lack of structural strength over the time, and their poor heat-conductive properties which prevent heat dissipation and may be the source of unwanted burning.